It is known to stop an engine of a motor vehicle while the vehicle is in motion in order to reduce emissions and fuel consumption. Such engine stops are performed automatically in the case of hybrid motor vehicles and free rolling stop-start vehicles when one or more predetermined conditions exist. A free rolling stop-start motor vehicle is one in which the engine is stopped while the vehicle is in motion unlike a conventional stop-start motor vehicle in which the engine is only stopped when the motor vehicle is determined to be stationary. A hybrid motor vehicle is one in which the motor vehicle has at least two sources of motive power, namely an internal combustion engine (hereinafter engine) and one or more electric traction motors.
In both cases it is desirable in certain circumstances to stop the internal combustion engine in order to save fuel and reduce emissions.
One of the features of such free rolling engine stop-start and hybrid systems is that the engine is stopped and started more often than is the case with a conventional motor vehicle or a conventional stop-start vehicle due to the increased opportunities to stop the engine. Although this increased opportunity has significant fuel saving and emission reduction benefits it produces a much increased burden on the battery or electrical energy storage device. This is because every time the engine is restarted a starter motor has to be engaged to restart the engine causing a drain on the battery or electrical energy storage device used to power it and potentially utilizing a larger battery or electrical energy storage device than is ideal.
It has been proposed in U.S. Pat. No. 6,524,217 to use the inertia of the motor vehicle to restart the engine in certain circumstances by a method known as a bump start in which a clutch is engaged causing the motion of the motor vehicle to be transmitted back through the drive-line to the engine, thereby causing it to rotate at a sufficiently high enough speed to permit starting to occur.
It is a problem with a system as disclosed in U.S. Pat. No. 6,524,217 that because the vehicle speed only has to be that at which sufficient inertia is available to start the engine, jerking of the motor vehicle may occur which is unacceptable to many vehicle owners. It is a further disadvantage that over-revving of the engine could occur if the vehicle speed is higher than expected when the restart occurs.
The inventors herein have recognized the issues with the above approach and provide a method to at least partly address them. In one embodiment, a method of controlling an internal combustion engine of a motor vehicle comprises, in response to a request for a start-up of the engine, determining whether the motor vehicle is currently travelling at a vehicle speed within a predetermined range of speed and, if the motor vehicle is travelling within the predetermined range of speed, using the inertia of the motor vehicle to bump start the engine.
This has the advantage that the number of times the starter motor has to be used can be reduced, thereby reducing the additional wear on the starter motor compared to a conventional stop-start device. Further, by restricting the use of the bump start to predetermined vehicle speeds, over-revving of the engine, jerky starts, and/or undesired torque fluctuations may be avoided.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.